Butadiene is a monomer with the highest consumption in synthetic rubber industry as well as an important intermediate in producing synthetic resin and organic chemicals, which can be used in preparing butadiene-styrene rubber, butadiene rubber, acrylonitrile-butadiene rubber, chloroprene rubber, ABS resin and the like, and, in a little cases, it may be used in preparing sulfolane, 1,4-butanediol, hexanedinitrile, hexamethylene diamine, butadiene oligomer, the pesticide captan and the like. Butadiene can also be widely used as adhesive, gasoline additive and otherwise. Asia has become the main area in the world in need of butadiene, and the demand for butadiene is in steady increase each year.
The available butadiene in the market is mainly given by extraction of by-products from naphtha cracking. However, with the development in light ethylene raw material and coal-to-olefin technology, there would no longer be great increase in quantity of the naphtha cracking devices, indicating that the yield of butadiene in the future could not meet its increasing demand, resulting in a growing market gap. It is necessary to develop novel processes, which is independent on olefin cracking, for producing butadiene.
Industrialization of the technique of preparing butadiene through oxydehydrogenation of butylene has been realized in 1960s of the 20th century. The catalyst most used in oxydehydrogenation of butylene is ferric spinel catalyst. For instance, Petro-Tex Corp. (U.S.) has disclosed a process for oxydehydrogenation of butylene using ferric spinel catalyst with a conversion of butylene of 78-80% and a selectivity to butadiene of 92-95%. China has developed ferric spinel catalysts including B-02, H-198, W-201 and the like as well in 1980s of the last century, which have been used in industrial production.
Attractive advantages in using ferric spinel catalyst (e.g. ferrite catalyst) are small content of oxygen-containing organic compounds within the by-products generated and simple treatment of wastewater. However, it has also presented some disadvantages, for example, easy happening of complete oxidation and large formation of CO and CO2. Therefore, how to improve the selectivity of the ferrite catalyst is crucial.
A ferrite catalyst is provided with a structure of spinel AFe2O4 (A represents Zn, Co, Ni, Mg, Cu, etc.), and can be used in oxydehydrogenation reactions through oxidation and reduction of Fe ions and interaction between oxygen ions in crystal and gaseous oxygen. Among the ferrites, zinc ferrite, magnesium ferrite and manganese ferrite are more suitable for oxydehydrogenation of butylene, wherein zinc ferrite shows a higher selectivity to butadiene than that of other ferrites (E-Y. Qiu, L.-T. Weng, E. Sham, P. Ruiz, B. Delmon, appl. Catal., Vol. 51, Page 235, 1989).
It is known that the activity of a catalyst can be influenced by its preparation process and elementary composition, and the catalytic activity in oxydehydrogenation and the selectivity to butadiene of the catalyst can be enhanced by improving the preparation process, adding helpful metal elements or applying pro- or post-treatment on the catalyst.
For example, it has been reported in U.S. Pat. No. 3,937,748 by Petro-Tex Chemical Corp. that a ferrite catalyst prepared through co-precipitation with ammonia as a precipitant has higher catalytic activity and longer operation life as compared with those of ferrite catalysts prepared by high-temperature solid-state reaction. It has also been reported in Chinese patent applications CN1033013, CN1072110 and CN1088624 by Lanzhou Institute of Chemical Physics (Chinese Academy of Sciences) that ammonia can be used as a precipitant in preparing ferrite catalyst through co-precipitation, and all of these patent applications have discussed in detail of the effects of formulation, preparing process, and process parameters and the like of the ferrite catalyst on the performance of the catalyst.
Additionally, the performance of the ferrite catalyst can further be improved by adding other active components, for example, Ni, Co, Ba, Sr, K, Mo, Bi and so forth into the catalyst. Some metals can enter the framework of the spinel and replace Fe or Zn within the ferrite catalyst, and the presence of which changes the activity and selectivity of the catalyst, especially when Fe is substituted with Al or Cr, resulting in an evident enhance in catalyst activity (J. Mol. Catal. A, Vol. 125, Page 53, 1997).
In U.S. Pat. No. 4,058,577 it is described that when a zinc ferrite catalyst is added with a proper amount of manganese carbonate component, the stability, activity and selectivity of the catalyst can be greatly improved.
In U.S. Pat. No. 4,083,884 it is reported that by-products of acetaldehyde, furan, and acraldehyde etc. from the reaction can be reduced by adding 1-3% (by weight) of calcium oxide into the ferrite catalyst.
In U.S. Pat. No. 4,332,972 it is reported that after adding 1.5 wt % of zinc carbonate into the zinc ferrite catalyst, both the conversion and selectivity of the catalyst are greatly improved with a conversion of butylene of 71.9% and selectivity to butadiene of 93.6% after reacting for 572 hours.
Proper activating treatment on the catalyst can also improve the performance of the catalyst. For example, it has been reported in U.S. Pat. No. 4,150,064 that activating a ferrite catalyst with vapor at about 450° C. can improve the conversion and selectivity of the catalyst.
Attractive advantages of the ferrite catalyst are small content of oxygen-containing organic compounds within the by-products generated and simple treatment of wastewater. However, for the available ferrite catalysts, there is still room for improvement in both selectivity to butadiene and conversion of reaction. Furthermore, it is found that both the raw material butylene and the product butadiene are easy to be deep oxidized under the reaction temperature to generate CO2 and CO when available ferrite catalysts are used.
Therefore, there is still need in the art to develop a ferrite catalyst for preparing butadiene through oxydehydrogenation of butylene, wherein the catalyst not only presents high conversion of butylene and selectivity to butadiene, but also improves the situation of deep oxidation both in the raw material butylene and the product butadiene under the temperature for oxydehydrogenation with this ferrite catalyst.